As the saying goes, you never know what's enough until you know what's too much. Worst case you end up with too much power which is easily solved by downsizing the rotors.

Personally I think you'll be fine, I'm currently running a borrowed set of M810 Saints on the front (180mm rotor) to compare it to my old M755 4-pot XTs, bike is a hardtail that's used for trail riding. There's definitely more power and it took a bit of getting used to, but I wouldn't say it's too much. Works just fine, same as my old XTs, but with a different feel on the lever and it takes a lighter touch. I have to give the brakes back but next year, I plan to try a set of M820 Saints.